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<div><table cellspacing="0" cellpadding="0" align="left"><tbody><tr><td align="left" valign="top"><p><strong><em>Background</em></strong><strong>:<em> </em></strong>  AmpC β-lactamases are important cephalosporinases chromosomally encoded in many of <em>Enterobacteriaceae</em> and a few other organisms where they mediate resistance to cephalothin, cefazolin, cefoxitin and penicillins. The six different families of plasmid-mediated AmpC β-lactamases have been described, but no phenotypic test can discriminate among them. AmpC multiplex PCR has been successfully used to discriminate plasmid-mediated ampC specific families in organisms such as <em>Klebsiella pneumonia</em> and <em>Escherichia coli</em>. The aim of this study was to indicate the prevalence of AmpC β-lactamase genes by specifically designed primers through PCR test.</p><p><strong><em>Methods</em></strong><strong>:<em> </em></strong>  243 total clinical urine samples were collected, and 227 isolates were identified as <em>Escherichia coli</em> based on standard biochemical tests. Subsequently, the isolates were screened by disc diffusion and combined disc test for β-lactamase production. Resistant isolates were evaluated by PCR for ampC family determination. </p><p><strong><em>Results</em></strong><strong>:<em> </em></strong> Antibiotic resistance pattern were observed as follows: cefepime (%25), ceftazidime (%31), ceftriaxone (%37), cefotaxime (%38). The ratio of isolates was detected as ESBLs and AmpC producers were 34% and 5.2%, respectively. PCR performed on 12 selected isolates via phenotypic tests and the results revealed that among 12 isolates, 11 contained <em>bla</em>_CMY-42.</p><p> </p></td></tr></tbody></table></div><strong><em>Conclusion</em>:<em>  </em></strong>Unfortunately, antibiotic resistance has become an increasingly critical problem in many countries like Iran and occurrence of isolates co-expressing AmpC-β-lactamases and ESBLs can create serious problems in the future. As antibiotic options in the treatment of AmpC β-lactamases and ESBLs producing organisms are extremely limited, molecular screening by laboratories is suggested to reduce the risk of therapeutic defeat.